1. Field of the Invention
The present invention relates to a method of controlling a rotary cutter for cutting material of long size moving between a pair of rotating shears having shearing edges on its peripheral surface in a predetermined length by controlling a motor for driving the shears.
2. Description of Related Art
An apparatus shown in FIG. 5 is heretofore employed to cut steel plate or corrugated cardboard moving on a line in a predetermined exact length of sheet. The apparatus obtains a moving quantity of material 15, such as corrugated cardboard, moving from left to right in FIG. 5 at a speed V by integrating an output of a pulse generator 1 coupled with rollers 30. The moving quantity of the material 15, a rotating velocity of shearing edges 13 which is obtained from a pulse generator 11 coupled with the shearing edges 13, and a rotating quantity, obtained by integrating the rotating velocity are supplied to a control unit 12. A control command, produced on the basis of the time when a proximity switch 36 for the shearing edges 13 detects completion of cutting the material, is applied to a motor 9 so that the motor 9 drives the shearing edges 13 through a gearing mechanism 14.
This apparatus is now described in more detail. Referring to FIG. 6, a counter 2 produces a moving quantity LL of the material and a velocity calculator 3 produces a speed VL of the material on the basis of the signal from the pulse generator 1. On the other hand, a counter 8 produces a moving quantity LS of the shears and a velocity calculator 16 produces a velocity VS of the shears on the basis of the signal from the pulse generator 11. The material moving quantity LL and the shear moving quantity LS are supplied to an adder 17 to obtain .DELTA.L. The value .DELTA.L is supplied to a gain table number calculator 4 which supplies a table number I to a movement gain table 5 and a velocity gain table 6. The movement gain table 5 obtains a gain coefficient GL in accordance with the table number I to produce GL.multidot..DELTA.L. In the same manner, the gain table 6 produces GV.multidot..DELTA.V where the value .DELTA.V is an output of an adder 18 to which the shear velocity VS and the material speed VL are supplied. Thus, the material moving velocity VL, the moving quantity GL.multidot..DELTA.L, which is added on the basis of the .DELTA.L, and the velocity GV.multidot..DELTA.V are supplied to an adder 19 which produces a velocity command VR to control a velocity controller 7. A rotational number of the motor 9 is supplied to the velocity controller 7 from a pulse generator 10.
With such an apparatus, when a cut length of the material 15 is longer than a peripheral length of the shearing edges 13, the velocity command supplied to the motor 9 is as shown in FIG. 7. That is, the shear velocity VS with regard to the material velocity (line speed) VL is adjusted, and if a distance that the material 15 is moved until stopped after the shear edges 13 complete the cutting is L.sub.1, the control unit 12 produces only a constant deceleration command without feedback control during 0&lt;LL&lt;L.sub.1. If a distance that the material 15 is moved until the shearing edges 13 start to be accelerated after the shear edges 13 is once stopped after completion of cutting is L.sub.2 and the moving distance until syncronized with the velocity of the material 15 after acceleration is L.sub.3, the above value .DELTA.L is obtained and the velocity command is supplied to the speed controller 7 during L.sub.2 &lt;LL&lt;L.sub.3.
As basic commands to cut the material, it is required that a cut length is equal to a specified length and the line velocity in cutting is equal to a speed of the shear edges 13. Accordingly, it is required that an exactly constant length of material 15 is fed during from deceleration to acceleration of the shear edges 13 and the line velocity VL and the shear velocity VS coincide with each other at the time of cutting.
However, the prior art apparatus possesses the following problems.
(1) When the position gain is raised as compared with the velocity gain near the cut position to obtain an exact position, the line velocity VL does not coincide with the shear velocity VS upon cutting. Further, when the speed gain is raised to match the velocity, the accuracy of the cut length is degraded. Accordingly, fine adjustment is required to maintain the cutting performance and it is hence difficult to maintain the accuracy in an actual apparatus in which the line velocity VL is varied delicately.
(2) Acceleration and deceleration require large energy and hence energy efficiency is degraded.
(3) A large capacity motor and a drive system therefor are required.